Audio that starts after the video
An MP4 whose sound begins later than its picture, signalled the way cameras and editors write it.
How it should play
What a broken player shows
What goes wrong
The delay is dropped and the sound plays early, out of sync with the picture.
The file
- Container
- MP4, 6.499 s
- Size
- 5.5 MB
- Video
- H.264, 1920x1080, 30 fps
- Audio
- AAC, stereo, 48,000 Hz
- Expected
- plays correctly in any player
How it was verified
Built by the testsrc generator (gen v0.2) and verified with FFmpeg 7.1.5-0+deb13u1 and GStreamer 1.26.2 in snapshot 2026-11-02, before it was published: the file has the property this page describes, and decoding it gives the expected result.
With a token: the file, how exactly it was built, the full fact sheet, and the expected result the checker judges a player against.
Use it
# the public facts curl https://testsrc.com/v1/cases/edge/audio-starts-500ms-late.mp4 # the full fact sheet and the file, with your token curl -H "Authorization: Bearer $TESTSRC_TOKEN" \ https://testsrc.com/v1/cases/edge/audio-starts-500ms-late.mp4/facts curl -H "Authorization: Bearer $TESTSRC_TOKEN" -o audio-starts-500ms-late.mp4 \ https://testsrc.com/v1/files/edge/audio-starts-500ms-late.mp4 # play it through your player and check what it showed testsrc run --player libvlc edge/audio-starts-500ms-late.mp4
See the API reference for tokens, quotas and snapshots.
testsrc is in early access. Free for open-source projects, $99/month per organisation for companies.
Get early accessMore on timing and sync
- Opus in Matroska audioMatroska audioThe delay is ignored: the start is cut, or the timing is a few milliseconds off.
- MPEG-TS timestamps wrapping aroundMPEG-TSPlayback freezes, jumps or stops at the wrap, and the duration comes out wrong.
- MPEG-TS that doesn't start at zeroMPEG-TSThe duration shows as zero or nonsense, and the seek bar is unusable.
5 more cases on this with a token.